JPH022299B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to photoelectric conversion devices, particularly optical information input units of facsimile machines, digital copying machines, laser recording devices, etc., barcode reading devices, and other characters and images. The present invention relates to a solid-state photoelectric conversion device that is applied to reading devices and the like.

[Conventional technology]

Recently, with the trend toward miniaturization of the entire device, reproduction is being performed as a photoelectric conversion device applied to the optical information input section of facsimile machines, digital copying machines, laser recording devices, etc., or other devices that read characters and images written on manuscripts. It has a light-receiving surface of a size equal to or close to the size of the original image to be displayed, has excellent resolution, can faithfully read the original image, and has a compact so-called elongated light-receiving surface. Significant progress has been made in the development of solid-state photoelectric conversion devices.

[Problems to be solved]

However, the photoelectric conversion device having the elongated light-receiving surface as described above has a major problem in the signal processing circuit section included in the photoelectric conversion section.

That is, the signal processing circuit section occupies a much larger area than the photoelectric conversion section, and by making the photoelectric conversion section longer, the optical path length of the optical information signal input to the light receiving surface can be extremely shortened. The point is that the advantage of miniaturization resulting from being able to do this is not fully utilized.

Normally, one way to solve this problem is to divide the photoelectric conversion elements (pixels) of the photoelectric conversion unit into multiple blocks, wire each block in a matrix, and provide each block with a common signal processing circuit. , a system is adopted in which this signal processing circuit section is operated in units of one block.

The problem with this matrix wiring is that a bonding process is required to connect each photoelectric conversion element and the signal processing section and take out the signal to the outside. If the parts were not integrated, the number of bonding steps would be extremely large.

Normally, to solve this problem, a signal processing circuit section is provided on a crystalline Si substrate, and a photoelectric conversion section is fabricated on top of the signal processing circuit section in order to integrate the signal processing circuit section.

However, since the light-receiving surface of the photoelectric conversion unit is becoming longer, it is necessary to provide a signal processing unit adjacent to the photoelectric conversion unit, and using a crystalline Si substrate is not sufficient to meet this requirement. .

〔the purpose〕

An object of the present invention is to improve conventional photoelectric conversion devices and provide a photoelectric conversion device that is smaller and longer and has excellent productivity and reliability.

Another object of the present invention is to eliminate any defects among the large number of photoelectric conversion elements constituting the photoelectric conversion section. An object of the present invention is to provide a photoelectric conversion device that is elongated and solidified.

Still another object of the present invention is that a photoelectric conversion section having a long light-receiving surface and a signal processing circuit section that processes signals photoelectrically converted by the photoelectric conversion section and outputs them in time series are mounted on the same substrate. An object of the present invention is to provide a solid-state photoelectric conversion device that is arranged in parallel with the photoelectric conversion device.

[Means to solve problems]

To achieve the above object, the present invention has a photoelectric conversion unit having a light-receiving surface into which optical information is input, and comprising a large number of photoelectric conversion elements each having a semiconductor thin film arranged in an array; a charge storage section comprising a plurality of storage means for storing signal charges photoelectrically converted by corresponding photoelectric conversion elements;
A transfer transistor section provided for each storage means, which performs a switching operation to transfer the signals stored in the corresponding storage means, and includes a large number of transfer transistors each having a semiconductor thin film; insulated from the semiconductor layer. a number of transistors having a layer;
A BBD transfer section, which is equipped with a large number of capacitors each having an insulating layer, and which arranges and outputs the signals transferred from each storage means in time series; , characterized by having an insulating layer shared by the transistor and the capacitor of the BBD transfer section.

[Effect]

By configuring as described above, the device can be made smaller and longer, and reliability and productivity are significantly improved.

[Example of implementation]

FIG. 1 is a circuit diagram for explaining one electrical circuit of a preferred embodiment of the photoelectric conversion device of the present invention.

The photoelectric conversion device shown in FIG. 1 includes, for example, n photoelectric conversion elements PE, PE1,
A photoelectric conversion section consisting of PE2,...PEn, a transfer transistor section consisting of n transfer transistors SW, SW1, SW2,...SWn provided for each photoelectric conversion element PE, and n capacitors.
A capacitor section for charge storage consisting of CE, CE1, CE2,...CEn, and a transistor BD and a capacitor BCE whose semiconductor section is made of a thin film semiconductor.
Transfer BBD (Bucket Buigade) consisting of
It is equipped with a signal processing section consisting of a device.

To describe these structural relationships in more detail, n photoelectric conversion elements PE are arranged in rows at equal pitches.
is made integrally with the corresponding photoelectric conversion element PE on the same substrate, and is directly connected in series to the photoelectric conversion element PE,
n storage capacitors CE that store signal charges corresponding to optical input, and n switching transistors SW, SW1, which perform a switching function to transfer the signal stored in the storage capacitor CE to the transfer BBD section. SW2,...SWn and 2n thin film transistors BD1, BD2, BD3, BD4,
...BD2n and 2n capacitors BCE, BCE1,
It consists of BCE2, BCE3, BCE4,...BCE2n, and is composed of a transfer BBD for outputting signals transferred from each storage capacitor CE in time series.

The transfer BBD is a BBD cell in which two transistors BD and two capacitors BCE are connected alternately.
It has a configuration in which n BCs are connected in series.

That is, for example, for the first numbered BBD cell BC1, the drain of the transistor BD1 and the source of the transistor BD2 are connected, one electrode of the capacitor BCE1 is connected to this source-drain connection, and the other electrode is connected to the drain of the transistor BD1. is a transistor
Connected to the gate of BD1. capacitor
One electrode of BCE2 is connected to the gate of transistor BD2, and the other electrode is connected to the gate of transistor BD2.
connected to the drain of The drain of the transistor BD2 is connected to the source of the transistor BD3 constituting the adjacent BBD cell BD2.

In this way, n BBD cells BD are connected in series, and the signal transferred to each BBD cell is
By inputting the BBD drive signals φ1 and φ2, each signal is sequentially transferred to the right-adjacent BBD cell, so that each signal is output from the terminal Vout in a time-series manner.

To briefly describe the signal processing of the photoelectric conversion device shown in the circuit diagram shown in FIG. are accumulated at the same time. After that, the gate terminals of switching thin film transistors SW, SW1, SW2,...SWn for transfer
Apply a voltage signal to V _G to connect each storage capacitor CE
The signals accumulated in the transfer are transferred to each corresponding capacitor in the capacitor BCE that constitutes the BBD.
Transfer simultaneously to BCE1, BCE3, ...BCE (2n-1).

Capacitor BCE1, BCE3,...BCE (2n-1)
The signals input to Odd-numbered thin film transistors BD1, _{BD3 ,} ...BD (2n
-1) and even-numbered thin film transistor BD2,
By driving BD4,...BD2n alternately, the data is sequentially sent to the BBD cell on the right, and the terminal
Output from Vout in chronological order.

The photoelectric conversion element PE basically consists of a light-transmitting electrode provided on the light-receiving surface side, an electrode provided at a position facing the electrode, and a photoreceptor layer sandwiched between these two electrodes. be done.

The photoreceptor layer constituting the photoelectric conversion element PE is made of, for example, hydrogenated amorphous silicon (A-Si:H
), PbO, CdSe, Sb ₂ S ₃ , Se, Se
-Te, Se-Te-As, Se-Bi, ZnCdTe, CdS,
Cu ₂ S, amorphous germanium hydride (A-
It is composed of a photoconductive material that can be formed into a highly sensitive thin film, such as Ge:H (hereinafter referred to as H) or hydrogenated amorphous germanium silicon (hereinafter referred to as A-GexSi(1-x):H). In the present invention, the layer thickness of the photoreceptor layer is determined by the degree of absorption of the photocarrier caused by the incidence of optical information, but is usually 4000 Å to 4,000 Å.
It is desirable that the thickness be 2μ, preferably 6000Å to 1.5μ. In the present invention, elements of group A of the periodic table such as N, P, As, Sb, Bi, or B, Al, Ga,
The photoreceptor layer is formed of A-Si:H because of the advantage that it can be made n-type or p-type by doping with elements of group A of the periodic table such as In and Tl as impurities. is considered suitable. Thin film transistor SW for switching and BBD for transfer
The semiconductor layer constituting the thin film transistor BD is
For example, A-Si:H, A-Gi:H, A-Ge _x Si _1-x :
H, polycrystalline silicon, CdS, CdSe, Cd-S-Se
etc. are used.

In the present invention, the semiconductor layer is made of A-Si:H or polycrystalline silicon, since the resistance can be controlled by doping with impurities, and the photoelectric conversion (element PE) can be integrated on the same substrate. It is preferable to form

In the present invention, the thickness of the semiconductor layer constituting the thin film transistor is 4,000 to 4,000 mm, based on the depth of expansion of the depletion layer formed in the semiconductor layer of the thin film transistor.
1.5μ is preferred.

The substrate on which the photoelectric conversion section and the signal processing circuit section are formed is made of a translucent material, for example, when optical information is incident on the light receiving surface of the photoelectric conversion section from the substrate side. Such restrictions can be removed when optical information is incident from the light receiving surface side formed on the opposite surface to the substrate.

Suitable materials to be used as the substrate in the present invention are those that are commercially available or available as long as they have excellent flatness, surface smoothness, heat resistance, and resistance to various chemicals during manufacturing. There are many things that can be done. Specific examples of such substrate forming materials include glass, No. 7059 glass (manufactured by Dow Corning), transparent materials such as magnesia, beryllia, spinel, and yttrium oxide, aluminum, molybdenum, and special stainless steel JIS standard
Examples include non-transparent metal materials such as SuS) and tantalum.

Next, in accordance with the above, the photoelectric conversion section of the present invention, a capacitor section for charge storage connected thereto, a switching thin film transistor section for transfer, and a transfer thin film transistor section are constructed.
The specific structure of the BBD section will be explained in detail. FIG. 2 shows a plan view A and a cross section schematically showing a photoelectric conversion section, a capacitor section for charge storage, a switching thin film transistor section for transfer, and a BBD section for signal transfer, which are the main parts of the present invention as a preferred embodiment. Figure B (a cross-sectional view at AA in Figure 2A) is shown.

The photoelectric conversion units are arranged in a single row array on the substrate 201.
For example, P
Alternatively, an ohmic contact layer 202 made of A-Si:H doped with a dopant such as As is provided, and a non-doped A-Si:H layer is formed on the ohmic contact layer 202.
A photoreceptor layer 203 is provided. Above the photoreceptor layer 203 is provided an ohmic contact layer 204 similar to layer 202, and above it is provided an upper electrode 205.

In the present invention, since light is input from the side opposite to the substrate 201, the electrode 205 is formed of a transparent material such as ITO, _SnO2 , _{In2O3 ,} etc.

The storage capacitor CE connected to the photoelectric conversion element PE through the electrode 206 has an insulating layer 2 on top of the electrode 206.
07, and a grounded common electrode 208 is provided thereon. The insulating layer 207 is made of silicon totride or silicon oxide, for example, and is made with an appropriate thickness so as to have a desired capacitance.

The transfer switching thin film transistor SW connected to the photoelectric conversion element PE through the electrode 206 has its source electrode connected to one end of the electrode 206 and its drain electrode connected to the electrode 21.
3, and an ohmic contact layer 210-1, 210 between each electrode and the thin film semiconductor layer 209.
-2 are provided respectively, and on the semiconductor layer 209,
An insulating layer 211 and a gate electrode 212 are provided.
Examples of the material for forming the insulating layer 211 include silicon nitride (Si ₃ N ₄ ) or silicon nitride.
Oxide (SiO ₂ ) is used.

In the BBD section, a semiconductor layer 214 is provided on the substrate 201, a source/drain layer 216 is provided on it,
Every other source/drain layer 216 is provided in the semiconductor layer 214 with an ohmic contact layer 215 interposed therebetween, and is connected to the transfer switching thin film transistor SW section by an electrode 213. An insulating layer 217 made of, for example, silicon nitride or silicon oxide is laminated thereon, and an upper gate electrode 218 is provided on the insulating layer 217.

The common gate electrodes 218-1 and 218-2 of the thin film transistors constituting the BBD are arranged so that signals φ ₁ and φ ₂ are applied alternately to the semiconductor layer and the source/drain layer.

Each gate electrode 212 of the transfer switching transistor SW is connected in common.

The electrodes 205 of each photoelectric conversion element PE are commonly connected.

Signals are extracted by opening contact holes in the insulating layer above the source/drain layers of the final stage BBD cell and providing signal extraction electrodes connected to the source/drain layers.

FIG. 3 shows a preferred implementation example when the transfer switching thin film transistor SW has a large W/L (channel width/channel length), divided into a plan view A and a cross-sectional view B at BB in FIG. 3A. is shown.

As shown in FIG. 3A, a semiconductor layer 304 is provided in ohmic contact with the electrode 302, and a semiconductor 305 and a gate electrode 306 are provided thereon. As shown in FIG. 3A, the channel is provided parallel to the line V _G of the gate electrode 306 taken out in common, and the W/L can be increased compared to the example of FIG. 303
The overlapping portion between the gate electrode 306 and the gate electrode 306 is reduced, and the regulating capacitance can be reduced.

〔effect〕

The photoelectric conversion device of the present invention specifically explained above can be made smaller and longer, and reliability and productivity can be significantly improved.

[Brief explanation of drawings]

FIG. 1 shows a preferred first embodiment of the photoelectric conversion device of the present invention.
FIG. 2A is a schematic plan view for explaining the structure, and FIG. 2B is a circuit diagram of an embodiment example of FIG. 2A.
Schematic cross-sectional view taken at AA showing , Figure 3A
is a plan view schematically showing the structure of a modified example of the first embodiment, and FIG. 3B is a schematic cross-sectional view taken along BB shown in FIG. 3A. 201, 301... Substrate, 207... Insulating layer for storage capacitor, 209, 304... Semiconductor layer of thin film transistor for transfer, 214... Semiconductor layer of thin film transistor for BBD.

Claims (1)

[Scope of Claims] 1. A photoelectric conversion unit having a light-receiving surface into which optical information is input and comprising a large number of photoelectric conversion elements each including a semiconductor thin film arranged in an array; provided for each of the photoelectric conversion elements; A charge storage section consisting of a large number of storage means for storing signal charges photoelectrically converted by corresponding photoelectric conversion elements; provided for each storage means, and transferring signals stored in the corresponding storage means. a transfer transistor section that performs a switching operation for the transfer and includes a large number of transfer transistors each having a semiconductor thin film; a transfer transistor section that includes a large number of transistors that have a semiconductor layer and an insulating layer; and a large number of capacitors that have an insulating layer; a BBD transfer unit that arranges and outputs the signals transferred from each storage means in time series; and is provided horizontally and integrated on the same substrate, and the transistor and the capacitor of the BBD transfer unit are provided horizontally and integrated on the same substrate. A solid-state photoelectric conversion device characterized by having an insulating layer shared by the two.